Target generation device, and method for manufacturing filter structure

ABSTRACT

A target generation device may include a filter structure, a flange, a tank unit, and a nozzle section. The flange may accommodate the filter structure and contain a flow path passing through the filter structure. The tank unit may contain a space in communication with the flow path in the flange and store a predetermined target material. The nozzle section may be provided to the flange and in communication with the space in the tank unit through the flow path in the flange. The filter structure according to one embodiment of the present disclosure may include a filter of a porous material and a socket integrally formed with the filter.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a continuation application of InternationalApplication No. PCT/JP2014/079350 filed on Nov. 5, 2014. The content ofthe application is incorporated herein by reference in its entirety.

BACKGROUND

1. Technical Field

The present disclosure relates to a filter structure, a targetgeneration device, and a method for manufacturing the filter structure.

2. Related Art

In recent years, as the semiconductor processes are moved to finerdesign rules, transfer patterns for photolithography in semiconductorprocesses have been rapidly shifted to finer designs. In the nextgeneration, fine patterning of 60 nm-45 nm or fine patterning of 32 nmor less will be required. To meet the requirement for fine patterning of32 nm or less, for example, the development of a stepper has beenexpected which is a device for generating extreme ultraviolet (EUV)light of a wavelength of about 13 nm combined with reduced projectionreflective optics.

The following three devices have been proposed as EUV light generatingdevices: laser produced plasma (LPP) devices which use plasma generatedby irradiation of target substances with laser light, discharge producedplasma (DPP) devices which use plasma generated by discharge, andsynchrotron radiation (SR) devices which use synchrotron orbitalradiation.

CITATION LIST Patent Literature

Patent Literature 1: Japanese Patent No. 4854024

Patent Literature 2: Japanese Patent Application Laid-Open No.2013-140771

Patent Literature 3: Japanese National Publication of InternationalPatent Application No. 2008-532228

Patent Literature 4: U.S. Patent Application Publication No.2004/0071266

SUMMARY

A filter structure (110, 110A, 110B, 120, 130, 150, 160) according toone embodiment of the present disclosure may include a filter (111, 121,121A, 121B, 131, 151), and a socket (115, 126, 144, 156). The filter(111, 121, 121A, 121B, 131, 151) may contain a porous material. Thesocket (115, 126, 144, 156) may be integrally formed with the filter.

A target generation device (26) according to other embodiments of thepresent disclosure may include the above filter structure, a flange(301), a tank unit (260), and a nozzle section (266). The flange (301)may accommodate the filter structure and contain a flow path passingthrough the filter structure. The tank unit (260) may contain a space incommunication with the flow path in the flange and store a predeterminedtarget material. The nozzle section (266) may be provided to the flangeand in communication with the space in the tank unit through the flowpath in the flange.

A method for manufacturing a filter structure according to otherembodiments of the present disclosure is a method for manufacturing afilter structure having a filter of a porous material and may includestacking the filter partly covered by a masking member; thermallyspraying an outer surface of the filter partly covered by the maskingmember with a material (1008) having substantially the same coefficientof thermal expansion as the filter; processing the material to partlyexpose the masking member; and removing the masking member.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the present disclosure will now be described withreference to the attached drawings as illustrative only.

FIG. 1 schematically illustrates a configuration of an illustrative LPPEUV light generation system;

FIG. 2 is a schematic view of an example of a schematic configuration ofa target generation device including a target supply unit illustrated inFIG. 1;

FIG. 3 is a cross-sectional view of an example of a schematicconfiguration of a filter portion;

FIG. 4 is a cross-sectional view of an example of a schematicconfiguration of a filter portion according to Embodiment 1;

FIG. 5 is a cross-sectional view of an example of a schematicconfiguration of a multilayer filter according to the first modificationof Embodiment 1;

FIG. 6 is a cross-sectional view of an example of a schematicconfiguration of a multilayer filter according to the secondmodification of Embodiment 1;

FIG. 7 is a cross-sectional view of an example of a schematicconfiguration of a filter portion according to Embodiment 2;

FIG. 8 is a perspective view of an example of a schematic configurationof a filter structure illustrated in FIG. 7;

FIG. 9 illustrates a cross-sectional structure of the multilayer filterin the filter structure in FIG. 8 along a face perpendicular to adirection in which an internal space extends;

FIG. 10 illustrates a cross-sectional structure of a multilayer filterof the first modification of Embodiment 2 along a face perpendicular tothe direction in which the internal space extends;

FIG. 11 illustrates a cross-sectional structure of a multilayer filterof the second modification of Embodiment 2 along a face perpendicular tothe direction in which the internal space extends;

FIG. 12 is a cross-sectional view of an example of a schematicconfiguration of a filter portion according to Embodiment 3;

FIG. 13 illustrates a cross-sectional structure of the multilayer filterin the filter portion in FIG. 12 along a face perpendicular to thedirection in which the internal space extends;

FIG. 14 is a cross-sectional view of an example of a schematicconfiguration of a filter portion according to Embodiment 4;

FIG. 15 is a cross-sectional view of an example of a schematicconfiguration of a filter portion according to Embodiment 5;

FIG. 16 is a cross-sectional view of an example of a schematicconfiguration of a filter portion according to Embodiment 6;

FIG. 17 is a flow chart of an example process for manufacturing a filterstructure according to Embodiment 6 by thermal spraying;

FIG. 18 is a process cross-sectional view (1) illustrating themanufacturing process illustrated in FIG. 17;

FIG. 19 is a process cross-sectional view (2) illustrating themanufacturing process illustrated in FIG. 17;

FIG. 20 is a process cross-sectional view (3) illustrating themanufacturing process illustrated in FIG. 17;

FIG. 21 is a process cross-sectional view (4) illustrating themanufacturing process illustrated in FIG. 17;

FIG. 22 is a process cross-sectional view (5) illustrating themanufacturing process illustrated in FIG. 17; and

FIG. 23 is a process cross-sectional view (6) illustrating themanufacturing process illustrated in FIG. 17.

EMBODIMENTS

Contents

-   1. Overview-   2. General description of EUV light generation system    -   2.1 Configuration    -   2.2 Operation-   3. Terms    -   3.1 Terms in Section 2    -   3.2 Terms in disclosures-   4. Target generation device    -   4.1 Configuration    -   4.2 Operation-   5. Filter portion    -   5.1 Configuration    -   5.2 Operation    -   5.3 Problem to be Solved-   6. Embodiment 1    -   6.1 Configuration    -   6.2 Effect-   7. Modifications of Embodiment 1    -   7.1 Configuration    -   7.1.1 First modification    -   7.1.2 Second modification    -   7.1.3 Other modifications    -   7.2 Effect-   8. Embodiment 2    -   8.1 Configuration    -   8.2 Effect-   9. Modifications of Embodiment 2    -   9.1 Configuration    -   9.1.1 First modification    -   9.1.2 Second modification    -   9.2 Effect-   10. Embodiment 3    -   10.1 Configuration    -   10.2 Effect-   11. Embodiment 4    -   11.1 Configuration    -   11.2 Effect-   12. Embodiment 5    -   12.1 Configuration    -   12.2 Effect-   13. Embodiment 6    -   13.1 Configuration    -   13.2 Effect-   14. Materials    -   14.1 Materials for socket and cap    -   14.2 Filter material-   15. Process for manufacturing filter structure by thermal spraying

Embodiments of the present disclosure will now be described in detailwith reference to the drawings. The embodiments below are to be taken asmerely examples of the present disclosure and do not limit the scope ofthe present disclosure. In addition, not all the configuration and theoperation described in each embodiment are not necessarily essential tothe configuration and the operation of the present disclosure. It shouldbe noted that the same components are denoted as the same referencenumeral and overlaps between their descriptions will be omitted.

1. Overview

An embodiment of the present disclosure may relate to supply of a targetmaterial for EUV light generation, particularly to a target generationdevice for supplying a target material to a chamber for EUV lightgeneration. During supply of target material, a target material shouldbe accurately and stably supplied to a region where a plasma thatradiates EUV light is generated. However, particles present in thetarget material and the like may destabilize the supply of the targetmaterial to the plasma generated region. In view of this, embodiments ofthe present disclosure described below illustrate a target generationdevice for stable supply of a target material. Note that the presentdisclosure should not be limited to these factors and may relate to anyfactors for a target material for EUV light generation.

2. General description of EUV light generation system

2.1 Configuration

FIG. 1 schematically illustrates a configuration of an illustrative LPPEUV light generation system. An EUV light generating device 1 may beused with at least one laser apparatus 3. In this application, a systemincluding the EUV light generating device 1 and the laser apparatus 3 isreferred to as an EUV light generation system 11. As illustrated in FIG.1 and described later in detail, the EUV light generating device 1 mayinclude a chamber 2 and a target supply unit 26. The chamber 2 may be ahermetically sealable. The target supply unit 26 may be mounted, forexample, passing through the wall of the chamber 2. A target substancematerial supplied from the target supply unit 26 may be tin, terbium,gadolinium, lithium, xenon, or any combination of two or more of them;however, this is not necessarily the case.

The wall of the chamber 2 may have at least one through hole. Thethrough hole may be provided with a window 21 and pulse laser light 32from the laser apparatus 3 may pass through the window 21. The chamber 2may contain an EUV condenser mirror 23 having a spheroidal reflectivesurface. The EUV condenser mirror 23 may have first and second focuses.For example, a multi-layer reflective film with alternating molybdenumand silicon layers may be formed on the surface of the EUV condensermirror 23. For example, the first focus of the EUV condenser mirror 23is preferably located in a plasma generated region 25 and its secondfocus is preferably located at an intermediate light collection point(IF) 292. A through hole 24 may be provided in the center of the EUVcondenser mirror 23 and pulse laser light 33 may pass through thethrough hole 24.

The EUV light generating device 1 may include an EUV light generationcontrol device 5, a target sensor 4, and other components. The targetsensor 4 may have an imaging function and be configured to detect thepresence, path, position, speed, and other information on the target 27.

The EUV light generating device 1 may further include a connectingportion 29 that establishes communication between the interior of thechamber 2 and the interior of a stepper 6. The connecting portion 29 mayhave a wall 291 with an aperture 293 in the interior. The wall 291 maybe disposed so that its aperture 293 can be in the position of thesecond focus of the EUV condenser mirror 23.

The EUV light generating device 1 may further include a laser lighttravel direction controller 34, a laser light condenser mirror 22, atarget recovery unit 28 for recovery of the target 27, and othercomponents. The laser light travel direction controller 34 may includean optical element for defining the travel direction of the laser light,and an actuator for adjusting the position and the posture of theoptical element.

2.2 Operation

As illustrated in FIG. 1, pulse laser light 31 from the laser apparatus3 may pass through the laser light travel direction controller 34 andthen enter the interior of the chamber 2 through the window 21 as thepulse laser light 32. The pulse laser light 32 may travel to an insideof the chamber 2 along at least one laser light path, be reflected bythe laser light condenser mirror 22, and be radiated to at least onetarget 27 as pulse laser light 33.

The target supply unit 26 may be configured to output the target 27 tothe plasma generated region 25 in the chamber 2. The target 27 may beirradiated with at least one pulse of the pulse laser light 33. Thetarget 27 irradiated with the pulse laser light becomes plasma which cangenerate emitted light 251. EUV light 252 contained in the emitted light251 may be selectively reflected off the EUV condenser mirror 23. TheEUV light 252 reflected off the EUV condenser mirror 23 may be collectedat the intermediate light collection point 292 and then fed to thestepper 6. It should be noted that a single target 27 may be irradiatedwith more than one pulses of pulse laser light 33.

The EUV light generation control device 5 may be configured to controlthe entire EUV light generation system 11. The EUV light generationcontrol device 5 may be configured to process image data or the like ofthe target 27 captured by the target sensor 4. Further, the EUV lightgeneration control device 5 may be configured to control the timing anddirection of the ejection of the target 27, for example. Moreover, theEUV light generation control device 5 may be configured to control thetiming of lasing by the laser apparatus 3, the travel direction of thepulse laser light 32, and the position where the pulse laser light 33 iscollected, for example. These different controls are illustrative onlyand other controls may be optionally added.

3. Terms

3.1 Terms in Section 2

The terms used in the present disclosure are defined as follows. A“droplet” may be a drop of a dissolved target material. The shape of adroplet may be generally spherical. A “plasma generated region” may be athree-dimensional space predetermined as a space where plasma isgenerated.

3.2 Terms in Disclosures

In the description below, a cross section or cross-sectional view ofeach component of a target generation device may be, unless otherwisedesignated, a cross section or cross-sectional view including the pathsof droplets ejected from a nozzle hole. A “dense body” may be apoly-crystal or single-crystal body in which the orientations ofparticles of a ceramic are aligned for densification. A “multilayerdirection” may be a direction in which the layers of a multilayer bodyare stacked. An “upstream” and “downstream” of a flow path may refer toan “upstream” and “downstream” of the flow of a fluid in the flow path.

4. Target Generation Device

An example of a target generation device including the target supplyunit 26 illustrated in FIG. 1 will now be described in detail referringto a drawing.

4.1 Configuration

FIG. 2 is a diagram of an example of the schematic configuration of thetarget generation device including the target supply unit 26 illustratedin FIG. 1. As illustrated in FIG. 2, the target generation device mayinclude, in addition to the target supply unit 26, a pressure adjuster520, a temperature-controllable device 540, a controller 51, and apiezoelectric power supply 552.

The target supply unit 26 may include a tank unit 260, a filter portion300, a nozzle section 266, and a piezoelectric element 551.

The tank unit 260 may include a tank 261 and a lid 262. The tank unit260 may store a target material 271. The target material 271 may be tin(Sn) or other metal targets. A cylindrical projection 263 projectingtoward a chamber 2 (see FIG. 1) may be provided under the tank 261. Thisprojection 263 may be formed integrally with or independently of thetank 261.

The materials for the tank 261 and the projection 263, and the lid 262and the filter portion 300 may have low reactivity with the targetmaterial 271. This material having low reactivity with the targetmaterial 271 may be molybdenum (Mo), for example.

The filter portion 300 containing a multilayer filter 100 may beprovided at the bottom of the projection 263. A flow path passing fromthe tank 261 to the nozzle section 266 may be formed in the interiors ofthe projection 263 and the filter portion 300. The bottom of the filterportion 300 has an opening of this flow path. The details of the filterportion 300 will be mentioned later.

The nozzle section 266 may be provided covering the opening at thebottom of the filter portion 300. The nozzle section 266 may have anozzle hole 267. The nozzle hole 267 may be in communication with theflow path in the filter portion 300. The diameter of the nozzle hole 267may be, for example, 2 to 6 μm. The material for the nozzle section 266may be molybdenum (Mo).

The pressure adjuster 520 may include a pressure controller 525, anexhaust device 524, valves 521 and 522, and a pressure sensor 523. Theexhaust device 524 may be connected to an inert gas cylinder 530 via gaspiping 531. The cylinder 530 may have a valve 534 for adjusting thesupply gas pressure.

The valves 521 and 522 may be provided in two portions on the gas piping531. The gas piping 531 between the valves 521 and 522 may branch to gaspiping 532. The gas piping 532 may be in communication with the tankunit 260. The pressure sensor 523 may be provided to the gas piping 532.

The temperature-controllable device 540 may include a heater 541, atemperature sensor 542, a heater power supply 543, and a temperaturecontroller 544.

The heater 541 may be provided to heat the target material 271 in thetank unit 260. The heater 541 may be provided on the outer periphery ofthe tank 261. The temperature sensor 542 may be provided to measure thetemperature of the tank unit 260 or the target material 271 in the tankunit 260. The temperature sensor 542 may be provided on the side surfaceof the tank 261. The heater power supply 543 may supply current to theheater 541.

An output signal line extending from the controller 51 may be connectedto the piezoelectric power supply 552, the temperature controller 544,the pressure controller 525, and the EUV light generation control device5. An input signal line extending to the controller 51 may be connectedto the temperature controller 544, the pressure controller 525, and theEUV light generation control device 5.

4.2 Operation

The controller 51 of the target generation device illustrated in FIG. 2may conduct the following process upon reception of a droplet ejectionpreparation signal from the EUV light generation control device or acontroller of an external device.

In particular, the controller 51 may first control the pressure adjuster520 to exhaust the gas in the tank unit 260. Meanwhile, the pressurecontroller 525 in the pressure adjuster 520 may drive the exhaust device524 with the valve 521 closed and the valve 522 opened.

Subsequently, the controller 51 may control the temperature-controllabledevice 540 so as to melt the target material 271 in the tank unit 260.Meanwhile, the temperature controller 544 of thetemperature-controllable device 540 may drive the heater 541 so thatvalues detected by the temperature sensor 542 can be at or above apredetermined temperature Top. The predetermined temperature Top may beat or above the temperature of the melting point of tin (a temperatureof 232° C.) when the target material 271 is tin (Sn), for example. Inaddition, the predetermined temperature Top may be a range oftemperature. The range of temperature may be from 240° C. to 290° C.,for example.

The controller 51 may then determine if the values detected by thetemperature sensor 542 are at or above the predetermined temperature Topfor a predetermined time. If so, the controller 51 may provide the EUVlight generation control device 5 or the controller in the externaldevice with a notification that droplets are ready to be ejected.

Subsequently, upon reception of a droplet ejection signal requiring theejection of the droplets 27, the controller 51 may instruct the pressureadjuster 520 to increase the pressure in the tank unit 260 to apredetermined pressure P (e.g., 10 megapascals (MPa)). Upon reception ofthis instruction, the pressure controller 525 of the pressure adjuster520 halts the exhaust device 524 and opens the valve 521 with the valve522 closed, thereby introducing the inert gas in the cylinder 530 intothe tank unit 260. When the pressure in the tank unit 260 increases tothe predetermined pressure P, the pressure controller 525 may adjustopen/close of the valves 521 and 522 to perform a control formaintaining the pressure in the tank unit 260 at the predeterminedpressure P. While the pressure in the tank unit 260 is kept at thepredetermined pressure P, the target material 271 may be jetted out ofthe nozzle hole 267.

The controller 51 may then control the piezoelectric power supply 552such that the target material 271 jetted out of the nozzle hole 267changes into droplets in a predetermined size in a predetermined cycle.Consequently, desirable droplets may be supplied to the plasma generatedregion 25 (see FIG. 1) in the chamber.

5. Filter Portion

The filter portion 300 illustrated in FIG. 2 will now be described indetail referring to the drawings.

5.1 Configuration

FIG. 3 is a cross-sectional view of an example of the schematicconfiguration of the filter portion.

As illustrated in FIG. 3, the filter portion 300 may include a flange301, a multilayer filter 100, a filter holder 314, and at least one shim304.

The materials for the flange 301 and the filter holder 314 may have lowreactivity with the target material 271. This material having lowreactivity with the target material 271 may be molybdenum (Mo), forexample. The shim 304 may also be composed of a material (e.g., Mo)having low reactivity with the target material 271.

The flange 301 may have a cylindrical shape having the same diameter asthe projection 263. The flange 301 may be fixed to the projection 263 ofthe tank unit 260 with the use of a bolt not illustrated in the drawing.An O ring 304 for sealing may be provided between the flange 301 and theprojection 263. Note that the O ring 304 is optional. In other words,when plane sealing is formed between the flange 301 and the projection263, the O ring 304 may not be provided. Alternatively, both the O ring304 for sealing and plane sealing may be provided between the flange 301and the projection 263.

A flow path FL1 in communication with the flow path FL1 in theprojection 263 may be formed in the flange 301. The flow path FL1 in theflange 301 may have an enlarged portion to accommodate the multilayerfilter 100. The multilayer filter 100 may be securely accommodated inthe enlarged portion with the use of the filter holder 314 and at leastone shim 304. Thus, the multilayer direction of the multilayer filter100 may be substantially the same as the direction in which the flowpath FL1 in the flange 301 extends. The filter holder 314 and the shim304 may have a cylindrical or ring shape.

The surfaces of the flange 301 and the filter holder 314 in contact witheach other may be polished surfaces. In addition, both sides of the shim304, the surfaces of the projection 263 and the shim 304 in contact witheach other, and the surfaces of the filter holder 314 and the shim 304in contact with each other may be polished surfaces. These polishedsurfaces may be brought into contact with each other with the use ofplane sealing.

The multilayer filter 100 may filter particles of tin oxide and the likecontained in the target material 271. The multilayer filter 100 may havea multilayer structure with a plurality of filters. FIG. 3 illustratesthe multilayer filter 100 composed of three filters 101 to 103 as anexample.

The three filters 101 to 103 may be filters with filter hole diametersof 20 μm, 10 μm, and 6 μm, respectively, in sequence from the tank unit260 side, for example. The filters 101 to 103 may be a porous materialsuch as porous glass composed mainly of aluminum oxide- or silicondioxide-based glass.

5.2 Operation

During the operation of the filter portion 300, when the liquid targetmaterial 271 flowing from the tank unit 260 to the flow path FL1 passesthrough the multilayer filter 100, the particles in the target material271 may be filtered. This may remove the particles, which cause cloggingof the nozzle hole 267 and destabilize the paths of the droplets 27,from the target material 271 flowing to the nozzle section 266.

5.3 Problem to be Solved

When a porous material is used as a filter, friction due to thermalexpansion and shrinkage during assembly, heating, and cooling may causea partial loss of the filter and thus generate particles. Particles fromthe filter 103, for example, may not be removed by the multilayer filter100. These particles may reach the nozzle hole 267 and cause clogging ofthe nozzle hole 267 and destabilize the paths of the droplets 27. Inview of this, the embodiments below illustrate a filter structure, atarget generation device, and a method for manufacturing the filterstructure which can restrain the generation of particles from themultilayer filter 100.

6. Embodiment 1

Embodiment 1 may include an intermediate member for mounting themultilayer filter on the filter holder 314. Hereinafter, theintermediate member will be referred to as a socket.

6.1 Configuration

FIG. 4 is a cross-sectional view of an example of the schematicconfiguration of the filter portion according to Embodiment 1. Aconfiguration of the filter portion 300 different from the configurationin FIG. 3 will now be described.

As illustrated in FIG. 4, the filter portion 310 according to Embodiment1 may have the same configuration as the filter portion 300 illustratedin FIG. 3 except that it includes a filter structure 110 instead of themultilayer filter 100.

The filter structure 110 may include a multilayer filter 111 and asocket 115.

The multilayer filter 111 may have a disc-shaped multilayer structure.This multilayer structure may be formed by a multilayer formationprocess. The multilayer structure may consist of three layers. FIG. 3illustrates the case where the multilayer structure consists of threelayers of 112 to 114.

The layers 112 to 114 may be composed of porous materials with differentpore sizes. Alumina may be used as a porous material.

For the layers 112 to 114, the pore size may increase toward theupstream of the flow of the target material 271 (hereinafter alsoreferred to as the upstream in the multilayer direction). For example,the layer 112 in the most upstream of the flow of the target material271 may have a pore size of 12 μm. In this case, the pore size of thelayer 113 may be 0.8 μm. The layer 114 in the most downstream of theflow of the target material 271 may have a pore size of 0.2 μm.

At least one of the layers 112 to 114 may be thicker than the otherlayers. For example, the layer 112 may be thicker than the layers 113and 114. In this case, the layer 112 may act as a support for the layers113 and 114 and the entire multilayer filter 111.

For the layers 112 to 114, the thickness may increase toward theupstream of the flow of the target material 271. The thickness of thelayer 112 may be 2 mm In this case, the thickness of the layer 113 maybe 30 μm, and the thickness of the layer 114 may be 20 μm.

The socket 115 may have a shape that can hold the multilayer filter 111and can be accommodated in the filter holder 314. In this case, acontact between the socket 115 and the filter holder 314 may be presenton the periphery of the side surface of the socket 115 in order toprevent the leakage of the target material 271.

The socket 115 may be a ring member composed of a bulk of the samematerial as the multilayer filter 111. For example, the socket 115 maybe a dense alumina (alumina ceramic) body or single-crystal sapphire.

It should be noted that the porous rate of the layers 112 to 114 in themultilayer filter 111 may be, for example, 40 to 50%. Meanwhile, thesocket 115 may have a porous rate of, for example, 2% or less.

Surfaces of the socket 115 and the filter holder 314 in contact witheach other may be polished. This may provide plane sealing between thesocket 115 and the filter holder 314.

The multilayer filter 111 and the socket 115 may be integrally formed bybonding. When the multilayer filter 111 and the socket 115 are composedof alumina, they may be bonded by thermal bonding or glass bonding.Alternatively, the multilayer filter 111 and the socket 115 may bebonded with an alumina adhesive and then fired.

6.2 Effect

In the above-described configuration, the filter structure 110 in whichthe multilayer filter 111 and the socket 115 are joined may be mountedon the filter holder 314. When the multilayer filter 111 is joined tothe socket 115 in advance, the socket 115 is mounted on the filterholder 314. As described above, the socket 115 may be composed of adense ceramic or single-crystal material. Accordingly, a partial loss ofa porous material in the multilayer filter 111 due to friction can bereduced during assembly, heating, and cooling. Consequently, generationof particles during assembly, heating, and cooling, and thereforeclogging of the nozzle hole 267 and destabilization of the paths of thedroplets can be restrained.

7. Modification of Embodiment 1

FIGS. 5 and 6 illustrate modifications of the multilayer filter 111illustrated in FIG. 4. Configurations different from the configurationof the multilayer filter 111 in FIG. 4 will now be described.

7.1 Configuration

7.1.1 First Modification

FIG. 5 is a cross-sectional view of an example of the schematicconfiguration of a multilayer filter according to the firstmodification. As illustrated in FIG. 5, the multilayer filter 110A maybe a domical filter having a multilayer structure. In FIG. 5, thematerial (properties), pore size, porous rate and thickness of a layer112 a in the most upstream of the flow of the target material 271 may bethe same as those of the layer 112. Similarly, the materials(properties), pore sizes, porous rates and thicknesses of the layers 113a and 114 a may be the same as those of the layers 113 and 114,respectively.

7.1.2 Second Modification

FIG. 6 is a cross-sectional view of an example of the schematicconfiguration of a multilayer filter according to the secondmodification. As illustrated in FIG. 6, a multilayer filter 110B has thesame configuration as the multilayer filter 110A in FIG. 5 except thatits cylindrical portion in the dome is extended. This cylindricalportion may be separated from the inner surface of the socket 115. Thematerials (properties), pore sizes, porous rates and thicknesses of thelayers 112 b to 114 b may be the same as those of the layers 112 to 114,respectively.

7.1.3 Other Modifications

Modifications of the multilayer filter 111 may include, in addition tothe above-described modifications, components in a pyramid shape or anyother shapes.

7.2 Effect

The multilayer filter 111 having a domical or pyramid-shape may have alarger filtering area. This may improve the amount (rate) of the captureof particles from the target material 271. An increase in filtering areamay increase the cycle of the exchange of the multilayer filter.

8. Embodiment 2

In Embodiment 2, a hollow cylindrical multilayer filter may be used.

8.1 Configuration

FIG. 7 is a cross-sectional view of an example of the schematicconfiguration of the filter portion according to Embodiment 2. FIG. 8 isa perspective view of an example of the schematic configuration of thefilter structure illustrated in FIG. 7. FIG. 9 illustrates across-sectional structure of the multilayer filter in the filterstructure in FIG. 8 along a face perpendicular to the direction in whichthe internal space extends. A configuration of the filter portion 310different from the configuration in FIG. 4 will now be described.

As illustrated in FIG. 7, a filter portion 320 according to Embodiment 2may have the same configuration as the filter portion 310 illustrated inFIG. 4 except that it includes a filter structure 120 instead of thefilter structure 110.

As illustrated in FIG. 8, the filter structure 120 may include amultilayer filter 121, a cap 122, and a socket 126.

As illustrated in FIG. 9, the multilayer filter 121 may be a hollowcylindrical filter having a multilayer structure. The material(properties), pore size, porous rate and thickness of the outermostlayer 123 in the most upstream of the flow of the target material 271may be the same as those of the layer 112. Similarly, the materials(properties), pore sizes, porous rates and thicknesses of the layers 124and 125 may be the same as those of the layers 113 and 114,respectively.

As illustrated in FIG. 8, the opening at one end of the hollowcylindrical multilayer filter 121 in the longitudinal direction may besealed with a cap 122. The cap 122 may be a plate unit composed of abulk of the same material as the multilayer filter 121. For example, thecap 122 may be a dense alumina (alumina ceramic) body or single-crystalsapphire.

The socket 126 may be provided to the other end of the multilayer filter121 in the longitudinal direction. The socket 126 may have a shape thatcan hold the multilayer filter 121 and may be accommodated in the filterholder 314 without a space therebetween. The socket 126 may be composedof the same material as the socket 115 in Embodiment 1.

Surfaces of the socket 126 and the filter holder 314 in contact witheach other may be polished. This may provide plane sealing between thesocket 126 and the filter holder 314.

The multilayer filter 121 and the cap 122, and the multilayer filter 121and the socket 126 may be integrally formed by bonding. The bonding maybe performed in the same manner as the bonding between the multilayerfilter 111 and the socket 115 in Embodiment 1.

As illustrated in FIG. 7, the filter structure 120 having such aconfiguration may be mounted on the filter holder 314 such that the cap122 projects toward the flow path FL1 of the tank unit 260.

8.2 Effect

As in Embodiment 1, the filter structure 110 in which the multilayerfilter 111 and the socket 115 are joined can be mounted on the filterholder 314, thereby restraining generation of particles during assembly,heating, and cooling. This can restrain clogging of the nozzle hole 267and destabilization of the paths of the droplets.

9. Modification of Embodiment 2

The shape of the multilayer filter 121 according to Embodiment 2 is notlimited to a hollow cylindrical shape. Modifications are describedbelow.

9.1 Configuration

9.1.1 First Modification

FIG. 10 illustrates a cross-sectional structure of the multilayer filterof the first modification along a face perpendicular to the direction inwhich the internal space extends. As illustrated in FIG. 10, amultilayer filter 121A may have a regular hexagonal cross sectionincluding the flow path of the target material 271 in the center. Theshape of the cross section is not limited to a regular hexagon and maybe any polygon. The outline of the outermost layer 123 a and theoutlines of the inner layers 124 a and 125 a are not necessarilysimilar. To be specific, the layers 123 to 125 may have different crosssectional shapes. The materials (properties), pore sizes, porous ratesand thicknesses of the layers 123 a to 125 a may be the same as those ofthe layers 112 to 114, respectively.

9.1.2 Second Modification

FIG. 11 illustrates a cross-sectional structure of the multilayer filterof the second modification along a face perpendicular to the directionin which the internal space extends. As illustrated in FIG. 11, in amultilayer filter 121B, the outline of the outermost layer 123 b may beserrated with repeating recessed and protrude portions. The flow path ofthe target material 271 may be provided in the center. The outline ofthe outermost layer 123 a and the outlines of the inner layers 124 a and125 a are not necessarily similar. The materials (properties), poresizes, porous rates and thicknesses of the layers 123 b to 125 b may bethe same as those of the layers 112 to 114, respectively.

9.2 Effect

As described above, the shape of the cross section is changed toincrease the perimeter of the outline of the cross section of themultilayer filter, which may further increase the amount (rate) of thecapture of particles. The shape of the cross section of the multilayerfilter may be changed as appropriate depending on the manufacturingmethod. The polygonal multilayer filter 121A illustrated in FIG. 10, forexample, can be manufactured with a combination of plate-like members.The shape of the cap sealing the opening at one end of the multilayerfilter may be changed as appropriate depending on the shape of the crosssection of the multilayer filter.

10. Embodiment 3

In the configuration of Embodiment 2, the hollow cylindrical multilayerfilter may not project toward the tank unit 260 but the nozzle section266.

10.1 Configuration

FIG. 12 is a cross-sectional view of an example of the schematicconfiguration of the filter portion according to Embodiment 3. FIG. 13illustrates a cross-sectional structure of the multilayer filter in thefilter portion in FIG. 12 along a face perpendicular to the direction inwhich the internal space extends. A configuration of the filter portion320 different from the configuration in FIG. 7 will now be described.

As illustrated in FIG. 12, a filter portion 330 according to Embodiment3 may have the same configuration as the filter portion 310 illustratedin FIG. 7 except that it includes a filter structure 130 instead of thefilter structure 120. The filter structure 130 may have a configurationin which the portion of the filter structure 120 other than themultilayer filter 131 is vertically flipped.

As illustrated in FIG. 13, like the multilayer filter 121, themultilayer filter 131 may be a hollow cylindrical filter having amultilayer structure. For the layers 133 to 135 of the multilayer filter131, since the positional relationship between the upstream anddownstream of the flow of the target material 271 is inverted, theinnermost layer 133 may reside in the most upstream, and the outermostlayer 135 may reside in the most downstream. The materials (properties),pore sizes, porous rates and thicknesses of the layers 133 to 135 may bethe same as those of the layers 112 to 114, respectively.

10.2 Effect

The configuration according to Embodiment 3 can provide the same effectsand thus advantages as those provided by Embodiment 2.

11. Embodiment 4

In the above embodiment, the filter holder and the socket may beintegrally formed. A configuration of the filter portion 320 based onbut different from the configuration in FIG. 7 will now be described.Note that the integral formation of the filter holder and the socketillustrated in Embodiment 4 may be applicable to the other embodiments.

11.1 Configuration

FIG. 14 is a cross-sectional view of an example of the schematicconfiguration of the filter portion according to Embodiment 4. Asillustrated in FIG. 14, in a filter portion 340 according to Embodiment4, the filter holder 314 and the socket 126 illustrated in FIG. 7 arereplaced by the socket 144.

The socket 144 may have a shape that can hold the multilayer filter 121and can be accommodated in the flange 301. In this case, a contactbetween the socket 144 and the flange 301 may be present on theperiphery of the side surface of the socket 144 in order to prevent theleakage of the target material 271.

The socket 144 may be a ring member composed of a bulk of the samematerial as the multilayer filter 121. For example, the socket 144 maybe a dense alumina (alumina ceramic) body or single-crystal sapphire.

Surfaces of the socket 144 and the flange 301 in contact with each othermay be polished. This may provide plane sealing between the socket 144and the flange 301.

The multilayer filter 121 and the socket 144 may be integrally formed bybonding. When the multilayer filter 121 is composed of alumina and thesocket 144 is composed of alumina or single-crystal sapphire, they maybe bonded by thermal bonding or glass bonding. Alternatively, themultilayer filter 121 and the socket 144 may be bonded with an aluminaadhesive and then fired.

The socket 144 may have a groove to accommodate the shim 304. A surfaceof the flange 301 and a surface of the socket 144 in contact with eachother may be polished surfaces. A surface of the socket 144 and asurface of the shim 304 in contact with each other may be polishedsurfaces. These polished surfaces may be brought into contact with eachother with the use of plane sealing. When plane sealing is formedbetween the socket 144 and the projection 263, the shim 304 may not beprovided.

11.2 Effect

Embodiment 4 provides the same advantages as those provided by the aboveembodiments and allows a component consisting of the filter holder andthe socket to be replaced by one socket. Thus, the configuration of thefilter structure can be simplified. This can result in a reduction inthe cost of manufacturing the filter structure.

12. Embodiment 5

In the above embodiments, the socket may be formed by thermal spraying.A configuration of the filter portion 310 illustrated in FIG. 4 based onthe configuration in which the filter holder 314 and the socket 115 areintegrally formed and the socket is formed by thermal spraying will nowbe described. Note that the formation of the socket by thermal sprayingillustrated in Embodiment 5 may be applicable to the other embodiments.

12.1 Configuration

FIG. 15 is a cross-sectional view of an example of the schematicconfiguration of the filter portion according to Embodiment 5. Asillustrated in FIG. 15, a filter portion 350 according to Embodiment 5may have the same configuration as the filter portion 310 illustrated inFIG. 4 except that it includes a filter structure 150 instead of thefilter structure 110 and the filter holder 314.

In other words, the filter holder 314 and the socket 115 may be replacedby a socket 156. In addition, the multilayer filter 111 may be replacedby a multilayer filter 151.

The multilayer filter 151 may have a structure in which first to thirdfilters 152 to 154, which are different disc-like members, are stacked.The shapes, materials (properties), pore sizes, porous rates andthicknesses of the filters 152 to 154 may be the same as those of thelayers 112 to 114, respectively. Note that the multilayer filter 151 maybe replaced by the multilayer filter 100 or other multilayer filters.

The socket 156 may be a member formed by thermally spraying themultilayer filter 151. If the socket 156 is formed by thermal spraying,the filter structure 150 can be manufactured while the filters 152 to154 are held united. A process for manufacturing the filter structure150 by thermal spraying will be described later.

The socket 156 may have a shape that can hold the multilayer filter 151and can be accommodated in the flange 301. In this case, a contactbetween the socket 156 and the flange 301 may be present on theperiphery of the side surface of the socket 156 in order to prevent theleakage of the target material 271.

Like the flange 301, the socket 156 may be composed of a material (e.g.,Mo) having low reactivity with the target material 271.

Surfaces of the socket 156 and the flange 301 in contact with each othermay be polished. This may provide plane sealing between the socket 156and the flange 301. A surface of the socket 156 and a surface of theprojection 263 in contact with each other may be polished surfaces. Thismay provide plane sealing between the socket 156 and the projection 263.In this case, the shim 304 is not necessarily provided between thesocket 156 and the projection 263.

12.2 Effect

When the socket 156 is formed by thermal spraying so that the socket 156and the multilayer filter 151 can be integrally formed, the material for(properties of) the socket 156 may be determined independently of thematerial for (properties of) the multilayer filter 151. Accordingly, thematerial for (properties of) the socket 156 may be the same as thematerial for (properties of) the flange 301. When the socket 156 and theflange 301 are composed of the same material (properties), stress due toa difference in thermal expansion during assembly, heating, and coolingcan be reduced. Consequently, generation of particles during assembly,heating, and cooling, and therefore clogging of the nozzle hole 267 anddestabilization of the paths of the droplets can be restrained.

13. Embodiment 6

In the above embodiments, the multilayer filter may include a supportplate that increases stiffness. A configuration of the filter portion350 based on but different from the configuration illustrated in FIG. 15will now be described. Note that the support plate illustrated inEmbodiment 6 may be applicable to the other embodiments.

13.1 Configuration

FIG. 16 is a cross-sectional view of an example of the schematicconfiguration of the filter portion according to Embodiment 6. Asillustrated in FIG. 16, a filter portion 360 according to Embodiment 6may have the same configuration as the filter portion 350 illustrated inFIG. 15 except that the socket 156 further includes a support plate 165.

The support plate 165 may be a disc-like member having the same diameteras the first to third filters 152 to 154. The support plate 165 may becomposed of glass or other materials (e.g., Mo) having low reactivitywith the target material 271.

The support plate 165 may have a plurality of through holes in thecenter. The number of through holes may be, for example, 10 to 100. Thepore size of the through holes may be, for example, about 100 to 1500μm.

13.2 Effect

Since the multilayer filter 151 is supported by the support plate 165,the stiffness of the filter structure 160 can be increased. Hence, evenwith relatively high pressure on the target material 271 in the tankunit 260, for example, breakage of the multilayer filter 151 can berestrained.

14. Materials

In the above-described embodiments, alumina (or alumina ceramic) orsingle-crystal sapphire are described as example materials for themultilayer filter, the socket, and the cap. Other example materials willnow be described.

14.1 Materials for Socket and Cap

The materials for the socket and the cap preferably satisfy followingConditions 1 and 2.

-   (1) Having low reactivity with the molten target material 271 (e.g.    tin)-   (2) Having a coefficient of thermal expansion near that of the    flange 301

Table 1 illustrates example materials satisfying Condition 1.

TABLE 1 Coefficient of Filter thermal expansion Filter structureMaterial (×10⁻⁶/K) Metal filter Through hole Molybdenum 5.2 Through holeTungsten 4.6 Glass filter Porous glass Aluminum oxide- 6 silicon dioxideglass Quartz glass 0.59 Soda glass 8.5-9.0 Borosilicate glass 3.2Ceramic Porous ceramic Alumina 8.2 filter Silicon carbide 4.1 Tungstencarbide 5.2 Aluminum nitride 4.8 Zirconium boride 5.9 Boron carbide 5.4

As described above, a metal material for the flange 301 may bemolybdenum (Mo) having low reactivity with the target material (e.g.,tin). A material exhibiting a coefficient of thermal expansion near thatof molybdenum may be selected from Table 1 as a material for the socket.The coefficient of thermal expansion near that of molybdenum may be in arange ±20% of the coefficient of thermal expansion of molybdenum. Table1 illustrates such materials: silicon carbide, tungsten carbide,aluminum nitride, zirconium boride, and boron carbide.

14.2 Filter Material

The material for the multilayer filter may be the same as the materialfor the socket and have a different structure from that of the materialfor the socket. Alternatively, the material for the multilayer filtermay be different from the material for the socket. The material for themultilayer filter preferably satisfies following Conditions 3 and 4 inaddition to Conditions 1 and 2 for the materials for the socket and thecap.

-   (3) Able to have a porous structure-   (4) Bondable to the material for the socket or cap

A material satisfying Conditions 1 to 4 may be selected from Table 1 asa material for the multilayer filter. Alternatively, any other materialssatisfying Conditions 1 to 4 and having similar characteristics may beselected.

15. Process for Manufacturing Filter Structure by Thermal Spraying

A process for manufacturing a filter structure by thermal sprayingillustrated in Embodiment 5 or 6 will now be described referring to thedrawings. The description below takes a process for manufacturing thefilter structure 160 according to Embodiment 6 as an example.

FIG. 17 is a flow chart of an example process for manufacturing a filterstructure by thermal spraying. FIGS. 18 to 23 are cross-sectional viewsof the filter structure 160 during the main process, illustrating themanufacturing process illustrated in FIG. 17.

As illustrated in FIG. 17, in the process for manufacturing the filterstructure 160, a support plate 165 having a masking member 1006, a thirdfilter 154, a second filter 153, and a first filter 152 having a maskingmember 1003 may be bonded to each other with an adhesive (Step S101). Atthis time, as illustrated in FIG. 18, a third jig 1007 may be used as asupport. The adhesive may be a cyanoacrylate-based adhesive. Theadhesive may be any other adhesive which can be removed with a solutionand the like. This may result in a filter assembly 161 (see FIG. 18) inwhich the multilayer filter 151 consisting of the first to third filters152 to 154 is bonded to the support plate 165. The filter assembly 161may include the masking members 1003 and 1006.

As illustrated in FIG. 19, the entire outer surface of the filterassembly 161 may be thermally sprayed with a socket material to form athermal spraying portion 1008 (Step S102). The socket material may bemolybdenum. The thickness of the socket material after thermal sprayingmay be about 500 μm at most.

As illustrated in FIG. 20, the outer surface of the thermal sprayingportion 1008 may be then mechanically processed (Step S103). The outsidediameter of the thermal spraying portion 1009 after processing may bethe same as that of itself after completion of the filter structure 160.

As illustrated in FIG. 21, a ring member 1010 that allows the filterstructure 160 to engage with the flange 301 may be then welded to thethermal spraying portion 1009 (Step S104).

As illustrated in FIG. 22, the outside shape of a holding portion 1009may be then mechanically processed (Step S105). This may expose themasking members 1003 and 1006 of the filter assembly 161.

Portions of the welded ring member 1010 which is to be in contact withthe flange 301 and the projection 263 may be polished (Step S106).

As illustrated in FIG. 23, the exposed masking members 1003 and 1006 maybe removed with a solution (Step S107). This may complete the filterstructure 160. The adhesive may be then removed with a solution (StepS108).

The filter structure 160 may be then washed with pure water or the like(Step S109) and the amount of particles remaining on the filterstructure 160 after washing may be measured (Step S110). Washing of thefilter structure 160 may be repeated (Step S111: NO) until the measuredamount of particles falls within a predetermined allowable range (StepS111: YES).

The above description should not be construed to be limitations butillustrative only. Accordingly, it should be understood by those skilledin the art that modifications of the embodiments of the presentdisclosure can be made without departing from the attached claims.

The terms used in the entire description and attached claims should beconstrued to be “non-restrictive”. For example, the term such as“include” or “included” should be construed to mean “include, but shouldnot be limited to”. The term “have” should be construed to mean “have,but should not be limited to”. The indefinite article “a” in thedescription and attached claims should be construed to mean “at leastone” or “one or more”.

What is claimed is:
 1. A target generation device comprising: a filterstructure including a filter containing a porous material and a socketintegrally formed with the filter by bonding; a flange accommodating thefilter structure and containing a flow path passing through the filterstructure; a tank unit containing a space in communication with the flowpath in the flange and storing a predetermined target material; and anozzle section provided to the flange and in communication with thespace in the tank unit through the flow path in the flange, the filterhaving a porous rate higher than a porous rate of the socket.
 2. Thetarget generation device according to claim 1, wherein the filter andthe socket are integrally formed by thermal bonding.
 3. The targetgeneration device according to claim 1, wherein the filter and thesocket are integrally formed by glass bonding.
 4. The target generationdevice according to claim 1, wherein the filter and the socket areintegrally formed by thermally spraying the filter with a material forthe socket.
 5. The target generation device according to claim 1,wherein the filter and the socket contain materials having the samecoefficient of thermal expansion.
 6. The target generation deviceaccording to claim 1, wherein the filter and the socket contain the samematerial.
 7. The target generation device according to claim 1, whereinthe filter contains alumina, and the socket contains a dense aluminabody or a sapphire single crystal.
 8. The target generation deviceaccording to claim 1, wherein the socket contains a material containingat least one of molybdenum and tungsten, and the filter contains porousglass containing aluminum oxide-silicon dioxide glass.
 9. The targetgeneration device according to claim 1, wherein the filter has amultilayer structure including a plurality of layers having differentpore sizes.
 10. The target generation device according to claim 9,wherein among the plurality of layers, a layer on one side in amultilayer direction has the largest pore size, and a layer on the otherside in the multilayer direction has the smallest pore size.
 11. Thetarget generation device according to claim 1, wherein the filter has amultilayer structure with a plurality of filters having different poresizes.
 12. The target generation device according to claim 1, whereinthe filter has a disc shape.
 13. The target generation device accordingto claim 1, wherein the filter has a domical shape.
 14. The targetgeneration device according to claim 1, wherein the filter forms ahollow structure opened at both ends in a longitudinal direction, thetarget generation device further comprises a cap sealing an opening atone end of the filter in the longitudinal direction, and the socket isprovided at the other end of the filter in the longitudinal direction.15. The target generation device according to claim 14, wherein thefilter is circular in a cross section along a direction perpendicular tothe longitudinal direction.
 16. The target generation device accordingto claim 14, wherein the filter is polygonal or serrated in a crosssection along a direction perpendicular to the longitudinal direction.17. The target generation device according to claim 1, wherein thefilter has a multilayer structure including a plurality of layers havingdifferent pore sizes, the flange holds the filter such that a multilayerdirection of the filter is identical to a direction in which the flowpath in the flange extends, and among the plurality of layers, the layeradjacent to the tank unit along the flow path has the largest pore size,and the layer adjacent to the nozzle section along the flow path has thesmallest pore size.
 18. A method for manufacturing a filter structurehaving a filter containing a porous material and used in a targetgeneration device, comprising: stacking the filter partly covered by amasking member; thermally spraying an outer surface of the filter partlycovered by the masking member with a material having approximately thesame coefficient of thermal expansion as the filter; processing thematerial to partly expose the masking member; and removing the maskingmember.